Previous studies in the Thiele laboratory have identified the carboxyl- terminal transactivation (CTA) domain of yeast heat shock factor (HSF) as a critical region required for transcriptional activation of the yeast metallothionein gene CUP1 in response to heat and oxidative stress. This domain is dispensible for heat shock activation of the hsp70 gene family. Recently, I have determined that loss of this domain also results in a block in cell cycle progression, with arrest at G2 phase upon shift to 37 C. This is the first demonstration of a domain- specific role for HSF in cell cycle progression and is distinct from basal control of the essential family of hsp70 heat shock proteins. Based on its known role as a potent gene regulator, I predict that HSF controls the expression of genes required for cell cycle progression and division under conditions of thermal stress through the CTA. To further explore the roles HSF and potential target genes play in cell division during stress, I have taken a genetic approach and isolated both multicopy and extragenic suppressors of the temperature sensitive growth phenotype exhibited by strains lacking the HSF CTA (HSF(1-583)). I have identified the heretofore uncharacterized gene YCR030C as a multicopy suppressor of HSF(1-583) temperature lethality. I propose to characterize this gene and determine its mechanism for alleviating G2 arrest in this background with the ultimate goal of determining its relationship to HSF and cell cycle control. The phenotypic effects of inactivation of YCR030C will be investigated through gene disruption. Gene expression and localization studies of YCR030C will be conducted to determine the temporal and spatial coordination of the gene product with cell cycle progression. The role of YCR030C in transcriptional activation by HSF will be studied, and the ability of these two proteins to physically interact will be assayed by in vitro biochemical experiments. Furthermore, I will carry out a genetic screen for extragenic suppressors of the HSF(1-583) ts phenotype with the goal of isolating other genes which may link HSF with cell cycle progression during stress. The work described in this proposal links a critical stress-responsive transcription factor to a role in cell cycle progression.